1. Technical Field
The present invention relates to a fabrication method and a fabrication apparatus of a head using near field light mounted with a near field optical element.
2. Background Art
For information recording and reproducing apparatuses requiring an increase in capacity and reduction in size, magnetic recording techniques are demanded to achieve higher recording density. The higher the recording density becomes, the smaller a recording area per bit becomes, and the energy of one bit of information comes close to thermal energy at room temperature resulting in thermal fluctuations causing recorded information to be reversed or erased, for example.
In the in-plane recording method generally used in magnetic recording techniques, magnetism is recorded so that the magnetization direction is oriented in the in-plane direction of a recording medium. However, in this method, recorded information loss, for example, tends to occur because of thermal fluctuations as described above. Then, in order to avoid such failure, the recording method is shifting to the use of a perpendicular recording method in which magnetization signals are recorded in the direction perpendicular to the recording medium. This method is the method in which magnetic information is recorded according to the principles that a magnetic monopole is brought close to a recording medium. According to this method, a recording magnetic field is directed to the direction almost perpendicular to a recording film. Information recorded with the perpendicular magnetic field tends to keep stable energy because it is difficult that the north pole and the south pole form a loop in the recording film surface. Thus, this perpendicular recording method is more resistant to thermal fluctuations than the in-plane recording method.
However, recent information recording and reproducing apparatuses are demanded for much higher density. On this account, in order to suppress the influence of the magnetic domains adjacent to each other and thermal fluctuations to a minimum, such a recording medium having a stronger coercivity is being adopted as a recording medium. Because of this, even according to the perpendicular recording method described above, it becomes difficult to record information on the recording medium.
Then, in order to solve this problem, a hybrid magnetic recording method (near field light assisted magnetic recording method) is provided in which near field light locally heats a magnetic domain to temporarily reduce the coercivity for writing during this period. This hybrid magnetic recording method is the method that uses near field light generated by the interaction between a micro-area and a near field optical element formed on a near field optical head. The near field light is used to produce a light spot having a diameter of a few tens nm or below, which cannot be carried out by existent light because of diffraction limits, and to generate a heat spot in almost the same size.
In the near field optical element, a main problem is to obtain a strong micro-spot of the near field light. To this problem, some shapes are already proposed. In application 1 (JP-A-2001-118543), such a structure is formed in which the outline shape of an optical aperture provided at the tip end of a near field optical element is formed in a triangle and the polarization direction of the incident light is orthogonal to one side of the triangle, whereby a strong near field light is generated, which is localized on that one side (triangular aperture method). In the application 1 (Technical Digest of 6th international conference on near field optics and related techniques, the place country-region Netherlands, Aug. 27-31, 2000, p 100) and application 2 (JP-A-2002-221478), a metal film is formed on two surfaces facing to each other among four side surfaces of a quadrangular pyramid, these two surfaces have a gap below optical wavelengths near the top of the quadrangular pyramid, each of the metal films on the two surfaces has a top with the radius of curvature of a few tens nm or below in the gap part, and a strong near field light localized in the gap part is generated (bow tie antenna method).    Application 1: JP-A-2001-118543    Application 2: JP-A-2002-221478    Non-Patent Publication 1: Technical Digest of 6th international conference on near field optics and related techniques, the place country-region Netherlands, Aug. 27-31, 2000, p 100
In the foregoing techniques described above, for the near field optical element of the triangular aperture method in application 1, the fabrication method is already disclosed, and the element can be relatively easily fabricated. However, for the near-filed light element of the bow tie antenna method in Non-Patent Publication 1 and application 2, because the element requires processing of about a few nm to a few tens nm for shapes of the metal film top and the gap part, extremely advanced micromachining techniques such as an electron beam stepper (electron beam lithography system) and a focused ion beam apparatus are generally needed. For this, a simple fabrication method suited for mass production is sought.
In addition, it is also necessary that a near field optical element is incorporated in a head having an air bearing surface (ABS: air bearing surface) in accuracy of order of a few nm for floating in the air from a medium at a clearance from about a few nm to a few tens, and thus it is demanded to solve this by a fabrication method suited for mass production.